ABSTRACT
Objective To analyze the precision and stability of optical surface imaging system for patients who received radiotherapy with active breath control. Methods Eighteen radiotherapy patients with lung metastasis were managed by active breath control (ABC).The difference error detected by optical surface imaging system and CBCT were defined as the precision of optical surface imaging system. The variation among the error of optical surface imaging positioning the value of correction of treatment position and the error detected by optical surface imaging again were defined as the stability of optical surface imaging system. Intrafractional errors were analyzed by optical surface imaging system through whole treatment process (including breath hold and free breath). Results The optical surface imaging system had precision (systematic (Σ) and random errors (σ)) of 1.78/3.42 mm 2.54/6.57 mm and 2.79/3.22 mm respectively and stability of2.12/2.54 mm 3. 09/4.02 mm and 1.37/3.55 mm respectively in lateral-medial superior-inferior and anterior-posterior directions. The intrafractional errors (Σ and σ) were 0.42/0.85 mm 0.41/1.47 mm and 0.41/1.47 mm respectively for breath hold duration and 4.76/4.16 mm 6.54/7.78 mm and 3.13/5.92 mm for free breath duration in lateral-medial superior-inferior and anterior-posterior directions. Conclusions As an effective method for validate breath hold;Optical surface imaging system can improve the precision and safety of active breath control. However,the factors that affect the accuracy and stability of the optical surface imaging system in patients undergoing radiotherapy with ABC are not clear;it cannot replace the CBCT for positioning verification.
ABSTRACT
Objective To assess the impact of respiratory motion on the displacement of target area and to analyze the discrimination between free breathing and active breathing control (ABC) in patients with gastric cancer treated with post-operative radiotherapy. Methods From January 2005 to November 2006, 22 patients with post-operatively confirmed gastric cancer were enrolled in this study. All diseases were T_3/ N +, staging Ⅱ - Ⅳ. Patients were CT scanned and treated by radiation with the use of ABC. Image J software was used in image processing, motion measurement and data analysis. Surgical clips were implanted as fiducial marks in the tumor bed and lymphatic drainage area. The motion range of each clip was measured in the resultant-projection image. Motions of the clips in superior-inferior (S-I), right-left (R-L) and anterior-posterior (A-P) directions were determined from fluoroscopy movies obtained in the treatment position. Results The motion ranges in S-I, R-L and A-P directions were 11.1 mam, 1.9 mm and 2.5 mm (F = 85.15, P = 0. 000) under free breathing, with 2.2 mm, 1.1 mm and 1.7 nun under ABC (F = 17.64, P = 0. 000), and the reduction of motion ranges was significant in both S-I and A-P directions (t = 4.36, P = 0. 000;t = 3.73,P = 0.000). When compared with under free-breathing, the motion ranges under ABC were kept unchanged in the same breathing phase of the same treatment fraction, while significant increased in different breathing phase in all three directions (t = - 4.36, P = 0. 000; t = - 3.52, P = 0.000; t =-3.79, P = 0. 000), with a numerical value of 3.7 mm, 1.6 mm and 2.8 mm, respectively (F = 19.46, P = 0. 000) . With ABC between different treatment fractions , the maximum displacements were 2.7 mm, 1.7 mm and 2.5 mm for the centre of the clip cluster (F =4.07,P =0. 019), and were 4.6 mm, 3.1 mm and 4.2 mm for the clips (F =5.17 ,P =0.007). The motion ranges were significant increased in all the three directions (t = - 4.09, P=0.000 ; t =-4.46, P = 0.000 ; t = - 3.45, P =0.000). Conclusions In the irradiation of post-operative gastric cancer, the maximum displacement of organ motions induced by respiration is in S-1 direction and the minimum in R-L direction under free breathing. The use of ABC can reduce the motions significantly in S-I and A-P directions, and the same changes exist in both inter-and intra-fraction treatment.